The invention relates to a process for making a liquid evaporation retardant solution that when applied to the surface of a body of water exposed to the atmosphere forms thereon a two-dimensionally extensive interfacial structure called in the art a ‘monolayer’, ‘monomolecular film’, or ‘Langmuir film’.
An interested general reader may wish to consult the short informative discussion of monolayers accompanied by FIGS. 7.17, 7.18, and 7.19, in DESIGNING THE MOLECULAR WORLD, P. Ball (Princeton University Press, 1994).
Since early twentieth century work by I. Langmuir, E. K. Rideal, and others, monolayers research in laboratories has been advanced by occassional introductions of new techniques, for example, the laser interferometry method introduced by the present inventor, and referred to in LIPID AND BIOPOLYMER MONO-LAYERS AT LIQUID INTERFACES, K. S. Birdi (Plenum Press, 1989), which presents FIG. 4.32 to illustrate retardation of water evaporation from a surface by a hexadecanol and/or octadecanol monolayer. Hexadecanol and outadeoanol are non-ionic solids of substantial insolubility in water, and are straight-chain aliphatic alcohols having respectively sixteen and eighteen carbon atom molecular chains featuring a non-polar ‘tail’ section which is hydrophobia, and a smaller polar ‘head’ section which is hydrophillic.
The end position of the polar unit ‘head’ makes the higher aliphatic alcohols primary alcohols, as opposed to secondary. A secondary alcohol, isopropanol, for example, locates a corresponding unit centrally in its molecule. With the higher aliphatic alcohols, notwithstanding an unlikeness of their head and tail portions, the forces holding these parts together are a chemical bond of high energy and much larger than the physical association forces between the solute and the solvent alcohol, otherwise the separation that occurs in ionic compound dissolution would be evident which is not the case here.
Although hexadecanol and octadecanol are not the only compounds capable of forming monolayers that retard evaporation, they are the top two choices among those involved in practical water conservation efforts utilizing monolayers. Their reasonable cost and ready availability are assurred by large-scale manufacture to supply the bar soap, cosmetics, pharmaceuticals, lubricants, and several other sectors using these commercially so-called ‘heavy-cut detergent range’ aliphatic alcohols in large quantities.
RETARDATION OF EVAPORATION BY MONOLAYERS: TRANSPORT PROCESSES, editor V. K. La Mer, (Academic Press, 1962) contains astute discussions of theoretical aspects of monolayer formation and also several reports on a wide variety of methods tried by water conservation field workers for distributing monolayer forming materials, usually hexadecanol or octadecanol or a mix of the two, onto lakes and reservoirs. An important implication of the field reports is that when the laboratory research is left behind, fieldwork in water conservation encounters numerous problems that are complex and difficult both to assess with precision and to counteract effectively. Methods of investigation of monolayers conducted in the laboratory setting, including the inventor's own laser interferometry techniques, possess little applicability where the fieldwork is concerned, unfortunately.
In other words, techniques, materials, and research methodologies developed in laboratory work are generally not directly transferrable to problem-solving directed to practical end-use application of monolayer forming materials to conserve water supplies on the large scale After laboratory research initially revealed suppression of evaporation by films only a molecular length thick, in the early days of the art, there seemed assurred promise of great economies respecting quantity of monolayer forming material that would be needed to produce the interfacial structures in sizes covering even quite large lakes and reservoirs. Effective distribution of the material in environments featuring not only a large scale, but more significantly, uncontrolled conditions, proved to be a stumbling block.
A typical laboratory problem had been finding ways to apply to a water surface in a relatively small ‘Langmuir trough’ (shown in the Ball book by FIG. 7.17) an appropriately miniscule amount of the monolayer forming substance. Resolution of the problem involved making liquid solutions from which a solvent constituent serving as a bulking agent to render extremely small amounts of film former handleable would escape the water surface upon application of the solution thereto. A solvent much used in early work is benzene, however benzene proved to not escape the experimental region so thoroughly as intended. Another hydrocarbon solvent, hexane, proved to escape well and came into use as a spreading solvent in research work, such as that by the present inventor and others; for example, see “The effect of monolayers on the rate of evaporation of H2O and solution of OZ in H2O”, R. N. O'Brien et al, Canadian Journal of Chemistry 54, 2739, (1976), wherein hexane was the solvent.
Another solvent of known solution-making utility for adding bulk and to render distribution of a miniscule quantity of aliphatic film former maneageable in laboratory research is pure ethyl alcohol. Use of this short-chain alcohol is feasible not only in connection with distribution upon a Langmuir trough water surface, but has been used to study how a coating of aliphatic alcohol upon soil particles confers hydrophobicity, as reported by J. W. Kijne in “The action and durability of cetyl alcohol as an evaporation suppresant in soils”, Netherlands Journal of Agricultural Science 20, 145, (1972). The ethyl alcohol solution in that research contained as the solute 1% commercial ‘cetyl alcohol’ which was actually a mixture of 52% n-hexadecanol, 42% n-octadecanol, and 6% n-tetradecanol. J. W. Kijne no more proposed that large acreages of dry agricultural land should be soaked with a 99% ethyl alcohol solution, than I. Langmuir would have proposed adding benzene to public water supplies, or the present inventor would have proposed adding a hexane solution thereto instead. Laboratory-useable-solutions capable of depositing a monolayer-forming solute on a substrate in a small vial, dish, or Langmuir trough should not offhandedly be presumed utilitous for fieldwork applications.
Out at a lake or reservoir the theoretical amount of monolayer forming material for a given surface area coverage is not even particularly relevant as a guideline, since it is known never to be nearly enough. Naturally occurring uncontrolled factors cause substantial film forming materials losses, which are not really predictable, and it is known that the ordinary workers without exception agree on recourse to distributing an excess of material. The initial promise of economy respecting materials utilization rate has not proved realizable. The real material requirements for quantity of solute film former will tend to be large, not small. Therefore, if solute concentration is too low, in a solution using a solvent that is much more costly than the solute, the resulting diseconomy and impracticality of making and dispensing large amounts of such a solution to conserve water should not be ignored and/or glossed over by mere technical points such as that the solvent does, after all, dissolve the solute, thereby rendering a normal solid distributable in a liquified form.
A perception that the cost of a solvent would be excessive perhaps has contributed more than anything else to an important divide between two basically different technological approaches in the practical sector of water conservation by use of monolayers, namely: the divide between handling and distributing the film forming materials either in the solid state, the state of the higher aliphatic alcohols at standard temperature, or else to produce a liquid vehicle. Those choosing solids are relieved of concern with cost of a solvent, whereas those who espouse a solution route must attend to this concern. Further evident is a divide between intermittent re-distributions of evaporation retardant as necessary, after losses have occurred, or else providing for continuous steady distribution predicated on the idea that ongoing losses should be countered by ongoing replenishment. These two divides are not such as to absolutely exclude use of solids from continuous methods or exclude use of liquids from intermittent methods, but in general the solids distribution approach is better matched to intermittent rather than continuous operations.
Liquid forms of evaporation retardant compositions, more so than solids, tend with approximately equal ease to be distributable either by intermittent or continuous methods, as conditions warrant, affording a flexible balance of capabilities for meeting practically all causes of material and film loss. Besides inferior flexibility in this connection, it is known that particulate solids are susceptible to some causes of loss that either do not affect at all, or do not as seriously affect, distributed liquid forms of evaporation retardant.
One of the La Mer book reports tells how hexadecanol in a flaky solids form—as usually shipped by primary producers such as Proctor & Gamble—was in the dry summer of 195 manually scattered by volunteering boaters directly from shipping sacks onto Crystal Lake in Illinois, under supervision provided by Illinois State Water Survey Division worker, W. J. Roberts. The plan was to conduct the flake scattering operation intermittently, as often as necessary. The Crystal Lake experience seems only to have been feasible because lakeside-residing or nearby residing volunteers who owned boats were available, and because the material was considered cheap enough that measuring just how much should be scattered could be omitted. Manual scattering by a multi-boat fleet of volunteers has the drawback that major water supply reservoirs are often sited at great distance from habitations of prospective volunteers. However, the concept of distributing aliphatic alcohol solids unmixed with any other chemicals has also been given effect both in Australia and in America using powder blowing machines rather than fingered human hands to scatter waxy solid alcohol particles. With high-speed boats, big sprays of powder pluming out therefrom, the labor content of spreading operations is reduced.
Machine-blown plumes of solid particles tend to lose more particles carried aloft by adverse wind and transported to where they are not needed, namely ashore. The machines are more susceptible to clogging—by far—than are human fingers.
Two causes of material loss for solids distribution methods that do not affect liquid forms are ingestion of flakes and particles by minnows, and heavy microbial growths colonizing any particles missed by the minnows. An all-solids distribution approach can lose much of its advantage respecting cheapness if significant material quantities are wasted even before an evaporation retarding film can be established. Liquid forms permit film formation substantially without pre-film distribution lose.
Unfortunately, both basic distributionx of either an all-solids or a liquid form composition will face problems and causes of more losses after the monomolecular film of aliphatic alcohol is formed. Such a structure is a fragile entity which is not expected to long endure in natural outdoor settings. By chance there may occassionally occur favorable environmental conditions which extend film life. Tear and puncture resistance of a one molecule length thick film require highly sophisticated techniques to even measure, the magnitude is so low, and a film is susceptible to serious damage or outright disintegration by such simple uncontrolled events as hail, rain, choppy water, or even just flocks of birds alighting upon and afterwards taking off from a monolayer-covered lake or reservoir. As a response specifically to such transient and uncontrollable causes of film loss, there is merit to intermittent methods of film former distribution involving cessation of operations during periods when any film formed would tend to be destroyed as fast as formed.
Wind has not only the above mentioned airborne transportation effect on cast-through-the-air solids, but has a well known effect of propelling an already formed film itself along the water surface until it collapses onto a leeward shoreline. This is called ‘rafting’ in the art, and the collapse is called ‘retraction’. Steady even moderately low-velooity wind with a prevailing direction, which is not uncommon at reservoir sites, causes rafting leading to retraction about which nothing can practicably be done except to continuously distribute an excess of film forming material from the windward side. Here it can be easily seen that materials costs go up substantially. Liquid solutions are no more immune to the film destruction problem than any other form of evaporation retardant composition, making it imperative to keep the starting materials costs for solution making as low as possible.
Several if not all possible causes of film lose may be operative at one time, but the deadlier two film destroyers are the chop-caused outright disintegration and collapse onto the lee shore due to wind-propelled rafting. Additional and relatively minor losses of already formed film material are caused by photochemical degradation, oxidation, evaporation (not of underlying liquid but of the alcohol film), and even dissolution or blending into an underlying liquid body which is far from being the relatively pure water of laboratories. Suspended oily dirt and other particles may be present in a lake or in a reservoir downstream of an agricultural or industrial district. The hydrophobic tails of aliphatic alcohols are not lyophobic. To the contrary, they are oil-loving and if given an opportunity will attach to oily dirt particles riding in the water, instead of sticking up from the water surface. If heavy-cut detergent range aliphatic alcohols did not have this attraction of their molecular tails to oily dirt, they would be useless in many of the applications which provide the commercial incentive for their mass-production. The point here is that if encountering dirty water happens to be yet another loss-causing condition beyond the control of the water conservation worker, again about all he or she can be expected to do is apply an excess of the evaporation retardant composition.
One final film loss circumstance warranting mention is that reservoirs of the type having overflow spillways will drop their surface-borne film right over the spillway. In a swimming pool, certain drains flush with the surface do the same thing. Obtaining enduring coverage of certain types of a body of water, the surface of which is itself not the fixed-in-place entity it superficially appears to be, but instead constantly moves on, imperceptibly replaced by an identical surface, therefore will necessitate a continuous mode of evaporation retardant distribution, even if all other loss causing factors are absent.
The background discussion to this point is thought to have established the likelihood that larger than the theoretical quantities of evaporation retardant film forming materials are required in their practical utilization outside the laboratory.
Laboratory practitioners would not orinarily concern themselves over expense of a solvent for rendering miniscule amounts of aliphatic alcohol handleable, yet it is common for information about solvents to originate from laboratory work. Whether there does or does not eventuate a contribution to the patent literature, the same information is often disclosed in research papers. Possibly when Dr. Kijne, in his research paper cited above, mentioned use of an ethyl alcohol solution with a 1% aliphatic alcohol concentration, he did not realize that a solution of the same kind and with that concentration within its specified range had a half dozen years earlier received U.S. Pat. No. 3,273,957 for a METHOD OF RETARDING SURFACE EVAPORATION (Sept. 20, 1966), N. Beredjick, inventor.
Rather than proposing it to be altogether novel to dissolve an aliphatic alcohol in an obviously feasible solvent such as ethyl alcohol, etc., N. Beredjick focussed disclosure on data established by small scale experiments directed to aiding determination of an appropriate range for the concentration of film forming solute he sought as an improvement. Improvement was needed specifically because of there having been suggestions previously of concentrations in some range that did not work. The unworkable concentration range referred to, unfortunately, was not identified in this cited patent (BEREDJICK). However, in view that a concentration between only 0.1% and 2% solute was proposed by N. Beredjick, it seems reasonable to suppose that the unworkable concentration range suggestions had gone substantially higher, rather than lower. However high they went, those suggested concentrations had to N. Beredjick's personal knowledge caused two problems: 1. they destroyed film forming properties of the aliphatic alcohol solute; and, 2. they caused undesirable solute precipitation in containers subjected to wide temperature variation.
The data presented in Tables I and II (BEREDJICK) unfortunately do not reveal anything about propensity to solute precipitation; there is no disclosure of saturation level at standard temperature, let alone at a lower temperature where solubility is expected to decrease for most known types of true solutions. In the present inventor's opinion, it is scientifically required to address the issue of saturation level whenever a need to assess probability of solute precipitation is evident. Nevertheless, some previously unavailable data was produced, and and the cited prior art patent thus merits being accorded a real contribution to the art.
Specifically referring to Table II of N. Beredjick's patent, the data interestingly shows—for one thing—how very small a difference respecting the evaporation retarding outcome was found to obtain between an n-butanol solution with a 0.1% octadecanol concentration, and an isopropanol solution at the same 0.1% concentration of the same solute. If data had been presented on stabilities for the two close-in-effectiveness solutions at standard and then cold temperatures, the patent could then have indicated which one operates best for resolving the rather neglected one pf the two background problems raised in the second to last sentence of the third paragraph of the patent: undesired solute precipitation.
Essentially, the Beredjick invention proposes making non-aqueous alcoholic evaporation retardant solutions made in the concentrations of between 0.01% to 2% aliphatic alcohol as the monolayer forming solute, and from a minimum of 98% up to a high 99.99% concentration of short-chain alcohol as the solvent, preferring hexadecanol and/or octadecanol as solutes, and ethyl alcohol or else isopropanol as the solvents. In the present inventor's opinion, although a solution in accordance with these teachings is as technically feasible as would have been expected at the time of the disclosure, for the covering of 50 ml. water in three-inch diameter dishes, the teachings fail to afford an order of materials cost economy commensurate with justifying the large-scale use of an evaporation retardant made and distributed in the form of an alcoholic liquid solution. Above discussion of materials loss problems in the field explains exactly why this is the present inventor's opinion. The technical workers at the end-use sites invariably deal with the materials loss problems by distributing excess amounts of whichever composition has been recommended and supplied to them.
The Beredjick patent expressly permits the latitude of precise quantities calculation to the field workers, which is not a policy from which specifically the present inventor means to diverge; however, the present inventor has taken well into account the workers' known practices when devising the product with which they will be armed for combatting water evaporation.
Three brief remarks concluding the background of the present invention are now in order. First, it is expected that some urgent circumstance of drought will oneday require large quantities of evaporation retardants to be transported from the place of manufacture to where needed. A considerable distance of transport by truck, in such an instance, is envisioned. If it were generally adopted to employ a liquid alcohol solvent at so high a concentration as taught by N. Beredjick, viz. up to 99.99%, such a practice is considered by the present inventor to haul too much solvent and to be not so fitting to the end-use circumstance as would be use of a substantially cheaper solution capable of delivering a greater amount per truckload of the film forming material needed, hauling as little costly liquid alcohol solvent as is feasible.
Second, in any urgent case of need for a water conservation product especially, but also at any time, it is highly desirable to optimize the speed of production, striving for fast production. Nothing at all was taught in the cited prior art concerning how fast the solute dissolved. Supposing all other factors equal, comparing two effective products, it would always be justified to adopt the more quickly manufacturable solution.
Third, the second of the two problems raised in the close prior art Beredjick patent should not be neglected. If anything is to be done about a foreseeable prospect of undesired precipitate formation, what that is, to be done, calls for being specified clearly, instead of leaving it to between-the-lines conjecture—conjecture that, for example, supposes: if there is minimal amount of solute in the first place, that by itself may ensure that precipitation problems could hardly be major.